def generate(self, numRows):
        """
        :type numRows: int
        :rtype: List[List[int]]
        """
        if numRows==0:
            return []
        l1 = [[1]]
        n = 1
        while n<numRows:
            l1.append(map(lambda x,y:x+y, [0]+l1[-1], l1[-1]+[0]))
            n += 1
        return l1
print(generate(2,5))